Manufacture of sheets or films of cellulose material



Oct. 2, 1934. H. E. VAN DERHOEF 1,975,132

MANUFACTURE OF SHEETS OR FILMS OF CELLULOSE MATERIAL Filed Jan. 2, 1929 IN VEN TOR, Henry E Werlzoefi W W A TTORNEY Patented Oct. 2, 1934 UNITED STATES MANUFACTURE 1,975,132 F SHEETS on FILMS 0F CELLULOSE MATERIAL Henry E. Van Derhoef, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New York Application January 2,

22 Claims.

This invention relates to sheets and films prepared from solutions of cellulose esters or ethers.

In the preparation of sheet material containing cellulose products, the esters or ethers of cellulose are dissolved in suitable solvents with or without the addition of softeners or plastifiers,

and the viscous dope or solution thus produced is spread on a supporting surface. The sheet material is stripped from the supporting surface when it has cured sufficiently and is thereafter maintained in a suitable atmosphere until it is dry. It may, for example, be formed as a web which travels continuously from the point where it is stripped from the supporting surface through a drying chamber wherein the web is supported on suitable rolls. The web is thus maintained in.

a relatively taut condition during the drying. At

the completion of the drying operation, the web is removed and wound on reels or spools. In

2@ drying the sheet material, a considerable shrinkage occurs and the material is liable to distortion which renders it more or less unsuitable for use in the various purposes to which it is otherwise adapted.

It is the object of the present invention to provide a method of drying cellulose sheet and film material and to remove shrinkage in drying so that it will not take place later when the film is in use, (i. e., while being developed and fixed) 39 which represents a serious economic loss.

I have discovered that the drying may be accomplished effectively and that the difficulties heretofore encountered can be avoided if the material is subjected during drying to a relatively moist atmosphere, that is to say, if the air within the chamber in which the film is formed or cured is maintained in a sufliciently moist condition preferably near the point of saturation, by the introduction of steam or water vapor to the atmosphere. When the film or sheet is thus subjected to drying in the presence of a moist atmosphere, at a suitable temperature, the volatile' solvents in the material are removed more rapidly than under the usual procedure wherein the material is subjected to a dry atmosphere. The rapid removal of the volatile solvents causes a correspondingly rapid hardening of the sheet or film. Nevertheless, the surface of the dope is prevented from forming a hard skin which pre- 0 vents the interior solvents from escaping as readily as when there is no skin; the drying proceeds more uniformly and rapidly throughout the entire thickness of the sheet or film; when the curing is completed the support will shrink less there- 5 after due to the fact that the solvents, plastics,

1929, Serial No. 329,911

etc., have been more completely removed than in the ordinary method of curing; and distortion is avoided because such shrinkage as occurs develops uniformly throughout the sheet or film.

The temperature at which the drying is efiected may vary but should in general be such as to permit maintenance of a moist atmosphere. Con densation of the water vapor is to be avoided. The temperature, on the other hand, should not be maintained at a point above that required to accomplish the purposes, and I find that a temperature of approximately C. is most effective under usualconditions.

The operation can be carried on with a continuous web which travels through the drying chamber, or the film may be cut into sheets which may be suspended in the drying chamber and removed therefrom when the drying is completed.

I have found that the shrinkage resulting from drying in the manner described may decrease to Y the extent of 13% or more of the normal shrihkage in airdried film or sheets.

Any suitable apparatus may be employed in. the practice of the invention, as, for example, a simple drying chamber in which separate sheets 8 of the material may be suspended and to which steam or water vapor may be supplied; the chamber having means whereby the temperature therein may be regulated, as, for example, by the provision of steam or air-heating coils. Alternatively, and preferably, the air previously heated to the desired temperature and humidified by the introduction of steam or water vapor thereto, may be introduced continuously to the chamber and withdrawn therefrom to maintain an atmosphere having suitable characteristics for the accomplishment of the purpose of the invention.

Preferably in commercial operations, the film is dried in the form of a continuous web as it is withdrawn from the apparatus in which it is formed. Thus the film may be removed by a doctor from the forming roll and may pass directly into a drying chamber wherein it travels over a plurality of rolls back and forth through the chamber so that a relatively large area of the film continuously carrying with it the vapors of the solvents which may be condensed and recovered in any suitable apparatus.

The invention will be more readily understood by referring to the accompanying drawing which illustrates diagrammatically a drying chamber adapted for the treatment of a continuous web.

Referring to the drawing, the web 5 passes from the apparatus (not shown), in which it is formed, over a roll 6, which is enclosed with the apparatus, hereinafter described, in a suitable chamber wherein the drying atmosphere is maintained. The web is guided by a roll '7 and is threaded over a series of rolls 8 and 9 so as to pass continuously upwardly and downwardly in the drying chamber, both sides of the film thus being exposed to the moist atmosphere. A series of rolls 8 and 9 form a single unit. From this unit the film may be directed over a roll 10. It is guided by the roll '7 on to a roll 11'and thence by a roll 12 to the second unit, comprising rolls 13 and 14, which may be disposed in another compartment of the drying chamber. After passing upwardly and downwardly in this compartment, the film is directed by a roll 15 on to the roll 12 and thence over a roll 16 which may feed the film to the successive drying compartment. It will be understood that any desired number of drying units may be provided and that the film may continue through the successive compartments in which it is exposed to the moist drying atmosphere until the drying is completed. The film may be withdrawn from the final drying compartment and may be wound on a reel or spool as a finished product. The several compartments of the drying chamber may be supplied with air through pipes 17. The air may be heated and humidified prior to its introduction to the drying compartments in any suitable apparatus adapted for that purpose. The air may escape from the drying compartments through pipes 18 and may be conducted thereby to condensers or other means (not shown) in which the volatile solvents are'recovered.

The method as described may be applied to the preparation of film and sheet material from water-insoluble cellulose compounds which are soluble in suitable organic solvents and which may be utilized to prepare dopes capable of hardening and thus forming films. Such materials when converted into films and sheets may be dried rapidly and advantageously in the manner described with a maximum shrinkage while curing and with the avoidance of distortion.

The invention has the further advantage that the presence of water vapor in the atmosphere increases the electrical conductivity of the atmosphere. Consequently electro static charges cannot accumulate and'the damage of sparking and possible ignition of the volatile solvent vapors is eliminated.

The operation should be regulated in general to avoid over-heating of the film or sheet. The amount of steam or water vapor introduced may be such as to accomplish the desired drying most effectively. It should be insufficient, however, to effect wetting of the film or sheet or of the rollers over which the film passes. The film in the drying chamber should be under a slight tension, which, however, is insufficient to break or tear the web. The tension is easily regulated by controlling the speed of the large rollers over which the film passes and which provide frictionally the necessary traction effect to insure the continuous movement of the web.

Various changes may be made in the details of the procedure and with a proportioning of the -heat and moisture in the atmosphere of the drying chamber and particularly in the apparatus employed without departing from the invention or sacrificing any of the advantages thereof. For instance, the invention, as above explained, is applicable to the various stages of the curing operation commencing with the formation of the film from a solution. Whether the humid atmosphere is to commence contact with the film immediately upon its formation or at some stage thereafter or for any given span of the curing operation depends upon the rapidity and thoroughness with which it is desired to remove the solvent from the film and the extent to which later shrinkage of the film is to be avoided. If the humid atmosphere is to be introduced into the coating chamber wherein the film is first formed, it may not be desirable to employ a humid atmosphere throughout all of the curing chambers, depending upon the effect desired, as will be apparent to those skilled in the art. Other modifications will be equally apparent.

Having thus described my invention, what I claim as new and desire to secure by Letters Paten s:

1. The method of curing a cellulose derivative water-insoluble film which comprises subjecting the film to an atmosphere of high relative humidity immediately after the formation of the film and while it still contains a substantial percentage of solvent.

2. The method of curing a cellulose derivative water-insoluble film which comprises subjecting the film to a gaseous bath containing water in the vapor phase immediately after the formation of the film and while it still contains a substantial percentage of solvent.

3. The method of curing a cellulose derivative water-insoluble film which comprises subjecting the film to the action of steam immediately after the formation of the film and while it still contains a substantial percentage of solvent.

4. The method of curing a cellulose nitrate film which comprises subjecting the film to an atmosphere of high relative humidity immediately after the formation of the film and while it still contains a substantial percentage of solvent.

5. The method of curing a cellulose nitrate film which comprises subjecting the film to a gaseous bath containing water in the vapor phase immediately after the formation of the film and while it still contains a substantial percentage of solvent.

6. The method of curing a cellulose nitrate film which comprises subjecting the film to the action of steam immediately after the formation of the film and while it still contains a substantial percentage of solvent.

7. The method of curing a cellulose acetate film which comprises subjecting the film to an atmosphere of high relative humidity immediately after the formation of the film and whil it still contains a substantial percentage of solvent.

8. The method of curing a cellulose acetate film which comprises subjecting the film to a gaseous bath containing water in the vapor phase immediately after the formation of the film and while it still contains a substantial percentage of sol- 14o vent.

9. The method of curing a cellulose acetate film which comprises subjecting the film to the action of steam immediately after the formation of the film and while it still contains a substantial percentage of solvent.

10. The method of curing a cellulose ether film which comprises subjecting the film to an atmosphere of high relative humidity immediately 150 centage of solvent.

13. The method of treating a sheet or film of compositions containing water-insoluble cellulose derivatives consisting in maintaining the sheet or film immediately after it leaves the surface on which it is formed in a space which is charged with water vapor at a temperature preferably considerably above room temperature.

14. The method of treating a film of compositions containing water-insoluble cellulose derivatives which consists in passing the film, immediately after it leaves the surface on which it is formed, through a space charged with'water vapor at a temperature considerably above room temperature while the film is'in. an extended or taut condition. I

15. The apparatus for treating a film of compositions containing water-insoluble cellulose derivatives comprising a combination of a chamber, a plurality of guide rolls therein, means for ap= plying tension continuously to the film, and means for supplying the chamber with humidifled air.

16. The method of curing a cellulose derivative water-insoluble sheet which comprises subjecting the sheet to the action oi. water vapor.

17. The method of curing a cellulose derivative water-insoluble sheet containing a substantial proportion of solvent, which comprises subjecting the sheet to the action of water vapor.

18. The method of curing a cellulose derivative water-insoluble sheet which comprises passing the sheet after it leaves the surface on which it is formed through a space maintained charged with water vapor.

19. The method of curing a cellulose derivative water-insoluble sheet which comprises passing the sheet after it leaves the surface on which it is formed through a space maintained charged with water vapor at a temperature substantially above room temperature.

20. The method of curing a cellulose derivative water-insoluble sheet which comprises subjecting the sheet to the action of water vapor while maintaining it under tension.

21. The method of curing a cellulose derivative water-insoluble sheet which comprises subjecting the sheet to the action of water vapor at a temperature substantially above room temperature while the sheet is maintained in an extended, taut condition.

22. The method of curing a cellulose derivative water=-insoluble sheet which comprises passing the sheet after it leaves the surface on which it is formed through a space maintained charged with water vapor, and maintaining the sheet in an extended, taut condition while passing through the space maintained charged with water vapor.

HENRY E. VAN DERHOEF. 

